Endometrium 12mm is suitable for implantation, too thick or too thin endometrium will affect pregnancy. Endometrium 12mm is suitable for fertilized egg implantation, for pregnant women at this time the thickness of the endometrium is normal, the fertilized egg can adhere to the endometrium, and then implanted in the endometrium, which is conducive to the growth and development of the gestational sac. If the lining of the uterus is too thin or too thick, it will affect the implantation of the fertilized egg. If the lining of the uterus is too thin, the fertilized egg cannot be implanted into the uterine lining successfully, and it will be difficult to get pregnant. If the lining of the uterus is too thick, the implanted egg will not be able to reach the uterine fundus, and the fertilized egg will lose its nutrients which will lead to miscarriage, and it will be more difficult to let the woman get pregnant normally. A woman’s endometrium will change and vary with her menstrual cycle. After pregnancy, the endometrium will gradually thicken, usually within the range of 7-15mm, not too thin and not too thick. If the endometrium is too thin or too thick, it is not good for pregnancy. Any abnormality in the thickness of the endometrium should be dealt with in a timely manner.